title: Intrinsic uncoupling in the ATP synthase of Escherichia coli.
abstract: The ATP hydrolysis activity and proton pumping of the ATP synthase of Escherichia coli in isolated native membranes have been measured and compared as a function of ADP and Pi concentration. The ATP hydrolysis activity was inhibited by Pi with an half-maximal effect at 140 microM, which increased progressively up in the millimolar range when the ADP concentration was progressively decreased by increasing amounts of an ADP trap. In addition, the relative extent of this inhibition decreased with decreasing ADP. The half-maximal inhibition by ADP was found in the submicromolar range, and the extent of inhibition was enhanced by the presence of Pi. The parallel measurement of ATP hydrolysis activity and proton pumping indicated that, while the rate of ATP hydrolysis was decreased as a function of either ligand, the rate of proton pumping increased. The latter showed a biphasic response to the concentration of Pi, in which an inhibition followed the initial stimulation. Similarly as previously found for the ATP synthase from Rhodobacter caspulatus [P. Turina, D. Giovannini, F. Gubellini, B.A. Melandri, Physiological ligands ADP and Pi modulate the degree of intrinsic coupling in the ATP synthase of the photosynthetic bacterium Rhodobacter capsulatus, Biochemistry 43 (2004) 11126-11134], these data indicate that the E. coli ATP synthase can operate at different degrees of energetic coupling between hydrolysis and proton transport, which are modulated by ADP and Pi.
authors.affiliation: Department of Biology, Laboratory of Biochemistry and Biophysics, University of Bologna, Via Irnerio 42, 40126 Bologna, Italy.
authors.forename: Manuela
authors.initials: M
authors.lastname: D'Alessandro
authors.forename: Paola
authors.initials: P
authors.lastname: Turina
authors.forename: B Andrea
authors.initials: BA
authors.lastname: Melandri
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000609:Aminoacridines / Q000494:pharmacology; D025243:Bacterial Proton-Translocating ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology*; D005453:Fluorescence; D006868:Hydrolysis / Q000187:drug effects; D010710:Phosphates / Q000378:metabolism; D017494:Proton Pumps / Q000378:metabolism; D011770:Pyruvate Kinase / Q000378:metabolism
chemical_list: D000609:Aminoacridines; D010710:Phosphates; D017494:Proton Pumps; C010847:9-amino-6-chloro-2-methoxyacridine; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D011770:Pyruvate Kinase; D025243:Bacterial Proton-Translocating ATPases